Date of Award
Summer 8-15-2019
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
At ambient pressure Sm metal orders antiferromagnetically at 106 K and 14 K. The pressure-dependence of the magnetic ordering temperature To of Sm metal was determined through four-point electrical resistivity measurements in a diamond anvil cell to pressures as high as 150 GPa. A strong increase in To with pressure is observed above 85 GPa. In this pressure range Sm ions alloyed in dilute concentration with superconducting Y exhibit giant Kondo pair breaking. Taken together, these results suggest that for pressures above 85 GPa Sm is in a highly correlated electron state, like a Kondo lattice, with an unusually high value of To. A detailed comparison is made with similar results obtained earlier on Nd, Tb and Dy and their dilute magnetic alloys with superconducting Y. All four lanthanides enter an “unconventional” magnetic state under very high pressure. Resistivity measurements up to 45 GPa show that Cs, a member of heavy alkali metals, experiences a sharp resistance drop at Tc ≈ 1.4 K for pressures above 12 GPa. The value of Tc decreases upon the application of either a magnetic field or pressure. This result confirms the pressure-induced superconductivity for Cs nearly half a century ago reported by Wittig and significantly extends the pressure range studied. Parallel resistivity measurements are carried out on the lighter alkali metal Rb to 78 GPa pressure. Above 55 GPa Rb enters a superconducting state near 2 K where, as for Cs, Tc decreases in a magnetic field or pressure, Tc falling below 1.3 K above 85 GPa. In both Cs and Rb the superconductivity appears following a phase transformation from tI4 to oC16 with increasing pressure accompanied by a marked upturn in the room-temperature resistivity. The superconductivity, phase transition, and resistivity upturn are believed related to pressure-induced s-d electron transfer.
Language
English (en)
Chair and Committee
James S. Schilling
Committee Members
Erik Henriksen, Anne Hofmeister, Kenneth Kelton, Bryce Sadtler,
Recommended Citation
Deng, Yuhang, "Enhanced Magnetic Ordering in Sm Metal and Search for Superconductivity in Cs and Rb under Extreme Pressure" (2019). Arts & Sciences Electronic Theses and Dissertations. 1898.
https://openscholarship.wustl.edu/art_sci_etds/1898
Comments
Permanent URL: https://doi.org/10.7936/c88v-f658